I'm looking for a pattern or standard approach to the following example situation:
(hypothetical)
I want to set up a Class for Employee.
I then want to set up a class called EmployeeDB which handles database activities for an employee.
I have another class with common simple functions set up to do things like create formatted logfiles or send email alerts.

I have been trying to organize the different types of classes into differnet projects.
The problem is it seems to create circular references.

The Db class needs to reference the employee class to be able to return employee types. The employee class needs to be able to refernce the EmployeeDB class so that it can call the database methods.


 Should they just be in the same project to start with?


 Is there a differnet basic approach that would make more sense?

I use this approach:

Business entity layer project (BOL)
 - references: nothing
 - It will contain the Employee class.

Data access layer project (DAL)
 - references: BOL
 - Here will be a class for Employee data access (EmployeeDA)

Business logic layer project (BLL)
 - references: BOL, DAL
 - Here will be a class for Employee business logic methods. Initially, the methods may seem superfluous because all they really do is call the DAL to delegate responsibility. However, as you expand an application, you'll find that you need to perform more involved business logic on data that goes beyond just getting it from a database. The business layer is where it should go.

You application will need to reference the BLL and BOL, but possibly not the DAL because that's access entirely from the BLL.

Imar (a wrox author and regular poster here) has written a very thorough set of articles about multi-layer application architecture that you might find useful. It uses a very similar approach to what I have described above.

Part 1: http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=416
Part 2: http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=419
Part 3: http://imar.spaanjaars.com/QuickDocId.aspx?quickdoc=420


-Peter

I can confirm it does, as I discussed the concepts in great detail with Peter before I posted the final articles... ;)

Imar


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Imar Spaanjaars
http://Imar.Spaanjaars.Com
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